The present invention is related to the field of electrical circuit fabrication and especially to the field of printed circuit board fabrication employing a laser direct imaging device.
PCT patent publication WO 00/02424, the disclosure of which is incorporated herein by reference, describes a scanning laser direct imaging (LDI) system for writing an electric circuit pattern on a printed circuit board substrate.
FIG. 1 is a reproduction of FIG. 1 of the above referenced publication. Some details of its operation are given below. Further details of the operation and an explanation of the figure can be found in the publication. In such systems, a laser beam or beams, modulated with pattern data, is scanned across a sensitized printed circuit board substrate 78 to write a latent image of a desired electrical circuit pattern.
The substrate is optionally inverted and a second pattern in side to side alignment with the first pattern is written on the other side of the substrate. In accordance with some printed circuit board fabrication techniques, substrate layers may be sequentially laminated to previously produced substrate layers and an electrical circuit pattern is written on the outermost side of each sequentially added layer in a build up fashion. The latent patterns are developed to form etching masks on the substrate. The masked substrate is etched to form the desired electrical circuit pattern.
Among the problems which arise in printed circuit board fabrication is the side to side alignment of printed circuit patterns on various substrate layers, and mutual alignment among patterns printed on various substrate layers. One method utilized to obtain suitable alignment is disclosed in the embodiment of FIGS. 1, 2, 14, 15 and 16, of the publication (FIG. 2 is a reproduction of FIG. 14 of the above referenced publication.). PC board substrate 78 is formed with a plurality of holes 150 at least some of which are preferably aligned, at least roughly, in the scan direction. A base on which the substrate is mounted is formed with openings larger than the holes in the substrate and the holes in the substrate are positioned generally in correspondence to the openings in the base. One or more detectors 152 are positioned below the scan line of the scanner.
As the printed circuit board is transported past the scan line, the scanner scans across the holes in a substrate layer. Based on signals detected by detector 150 via the holes and the openings, the locations of the holes in the substrate layer with respect to the scanner are detected. The base is optionally rotated and scanning of the printed circuit board substrate then commences with the position of the scanning lines pattern being referenced to the location of the holes.
It should be noted that the position of the scanning beam that passes through holes 150 is scanned together with another beam that impinges a scale 80 that is used to determine the true instantaneous (scan dimension) position of the beam in the scan direction. Furthermore, the relative cross-scan position of the holes (and thus the board) is determined utilizing a second scale, typically operatively associated with the base.
When scanning the second side of the substrate, the procedure is repeated to determine the position of the holes and thus the position of the already scanned pattern on the first side of the substrate (or the position of already scanned patterns on lower layers in a build up board) with respect to the coordinate space of the LDI system. This allows for the data in the scanning of each subsequent side to be aligned with respect to previously scanned sides.
Optionally, an additional series of holes in the board and pins on the base, or a guide rail along the base, may be used for rough alignment of the substrate. Such pins are shown in FIG. 16 of the reference. In some conventional systems, only such mechanical means are used for aligning the patterns on the two sides of the substrate. The system may include means for rotating the board to improve alignment.
Measuring systems employing imagers, and especially CCD cameras, are known in the art for use in determining the positioning of a PC board in an LDI scanner. Generally, such cameras may be used to detect various markings on a printed circuit board laminate layer, or to detect an edge of a printed circuit board laminate layer and to relate the detected position of the marking or the edge with a scanner position.
An aspect of some embodiments of the invention is concerned with methods of calibrating the relationship between the coordinate space of a measuring system, for example, an imager and the coordinate space of an LDI scanner.
In some embodiments of the invention, a mark or a plurality of marks is written on light sensitive media by a scanner. The positions of the marks written by the scanner are used as a reference for calibration between the coordinate space of a measurement system and a coordinate space of the scanner. The substrate is then moved, in a controlled manner, to another location, at which the marks can be viewed by the measurement system, typically a camera. The positional relation in locations of the marks as written by scanner and measured by the measurement system, allows for correlation of the position of a mark in coordinate space of the measurement system to the position of the mark in coordinate space of the scanner.
In exemplary embodiments of the invention, the sensitized media is of a type which shows a visible change when exposed to the light used to scan a pattern on the board. This allows for the image of a mark written by the scanner to be visualized by an imager without development and without removing the substrate from the scanner.
Optionally, the marks written by the scanner in a calibration mode are 2-dimensional, and thus enable calibration and coordination of the field of view of the imager to the pixel grid of the scanner. An aspect of some embodiments of the invention is concerned with the calibration of the field of view of an imager, such as a camera, especially one used in a scanner for imaging patterns on printed circuit boards.
In many embodiments of the invention, the imager images patterns which may be extended in one or both X-Y dimensions and/or images having a number of features and/or a feature or features that are not centered on the field of view (FOV) of the imager. Due, inter alia, to distortions in the optics of the imager (which in an exemplary embodiment of the invention, is a camera, such as a CCD camera) and imprecise magnification, the physical location of a feature being imaged does not correspond to the coordinates of the feature on the image.
In some embodiments of the invention, the camera field of view is calibrated to correlate the pixel size and/or angular orientation of pixels in the camera to pixels in the scanner system.
An aspect of some embodiments of the invention is concerned with using an imager, such as a CCD camera, to determine the position of a printed circuit board substrate in a scanner.
In some embodiments of the invention, a plurality of stationary cameras or other imagers are used to perform the imaging function. In other embodiments a single stationary camera is used to image a plurality of features or a two dimensional feature (such as a corner) so that both position and angle of the substrate may be determined. In some embodiments of the invention, the one or more imagers (for example CCD cameras) are mounted on a rail or other accurate mechanism that allows movement of the camera in one dimension (generally in the scan direction, perpendicular to the movement of the substrate during writing). Movement along the rail may be measured accurately using an encoder, for example. Alternatively or additionally, the mechanism may be provided with precision xe2x80x9cdetentsxe2x80x9d or other fixed position determining mechanisms. In such systems, the imager position is limited to one or a few positions.
There is thus provided, in accordance with an exemplary embodiment of the invention a method of calibrating a camera used in a scanner for scanning images onto printed circuit board substrates, the method comprising:
(a) writing a pattern on a sensitized substrate using the scanner, wherein the pattern is visible without development;
(b) imaging the pattern with at least one imager; and
(c) determining a transformation between an imager referenced coordinate system and a scanner referenced coordinate system.
In an embodiment of the invention, the method includes moving the pattern between (a) and (b) without removing the substrate from the scanner. Optionally, the method includes measuring the amount of said movement and utilizing said measurement in said determination of a transformation.
In some embodiments of the invention, the at least one imager comprises a single imager. Alternatively, the at least one imager comprises a plurality of imagers.
In some embodiments of the invention, the at least one imager is fixed in position. Alternatively, the at least one imager is moveable, and including a measurement assembly for determining the position of the at least one imager.
Optionally, the pattern comprises a two dimensional pattern and including calibrating the field of view of the imager based on an image of the pattern acquired by the imager. Optionally, calibrating includes adjusting the spatial orientation of the imager with respect to the scanner. Alternatively or additionally, calibrating includes compensating for differences in magnification at various parts of the field of view of the imager. Alternatively or additionally, calibrating includes compensating for distortion in the field of view of the imager.
Optionally, determining a transformation includes determining coordinates of the pattern in imager space.
There is further provided, in accordance with another exemplary embodiment of the invention, a method of calibrating a field of view of a camera used in a scanner for scanning images onto printed circuit board substrates, the method comprising:
(a) writing a pattern on a sensitized substrate using the scanner, wherein the pattern is visible to the camera without development;
(b) imaging the pattern with the camera; and
(c) determining correction factors for locations in the camera field of view
Optionally, the pattern comprises a two dimensional pattern.
Optionally, calibrating includes adjusting the spatial orientation of the imager with respect to the scanner. Alternatively or additionally, calibrating includes compensating for differences in magnification at various parts of the field of view of the imager. Alternatively or additionally, calibrating includes compensating for distortion in the field of view of the imager.
There is further provided, in accordance with a preferred embodiment of the invention, a method of correcting a calibration of an imager used in a scanner for scanning images onto printed circuit board substrates, the method comprising;
(a) determining a transformation between an imager coordinate system and a scanner coordinate system;
(b) providing an element whose location can be separately determined utilizing the scanner beam and the imager;
(c) determining the location of the element in the imager coordinate system;
(d) transforming the location determined in (c) into the scanner coordinate system utilizing the transformation;
(e) determining an equivalent location of the element in the scanner coordinate system utilizing the scanner beam; and
(f) correcting the transformation based on a difference between the locations determined in (c) and (e).
In an embodiment of the invention, the method includes moving the pattern between (c) and (e) without removing the substrate from the scanner. Optionally, the method includes measuring the amount of said movement and utilizing said measurement in said determination of the equivalent location.
There is further provided, in accordance with an exemplary embodiment of the invention, a method of calibrating a camera used in a scanner for scanning images onto printed circuit board substrates, the method comprising:
(a) providing a pattern on a substrate;
(b) determining the coordinates of the pattern in a scanner coordinate system;
(c) imaging the pattern with at least one imager; and
(d) determining a transformation between an imager referenced coordinate system and a scanner referenced coordinate system.
In an embodiment of the invention, the method includes moving the pattern between (a) and (c) without removing the substrate from the scanner. Optionally, the method includes measuring the amount of said movement and utilizing said measurement in said determination of a transformation.
In some embodiments of the invention, the at least one imager comprises a single imager. Alternatively, the at least one imager comprises a plurality of imagers.
In some embodiments of the invention, the at least one imager is fixed in position. Alternatively, the at least one imager is moveable, and including a measurement assembly for determining the position of the at least one imager.
Optionally, the pattern comprises a two dimensional pattern and including calibrating the field of view of the imager based on an image of the pattern acquired by the imager. Optionally, calibrating includes adjusting the spatial orientation of the imager with respect to the scanner. Alternatively or additionally, calibrating includes compensating for differences in magnification at various parts of the field of view of the imager. Alternatively or additionally, calibrating includes compensating for distortion in the field of view of the imager.
Optionally, determining a transformation includes determining coordinates of the pattern in imager space.
In an embodiment of the invention, determining the coordinates of the pattern in a scanner coordinate system comprises:
scanning the hole pattern with the scanner; and
determining the positions of the holes as they pass the scanner.
There is further provided, in accordance with an embodiment of the invention, a method of calibrating a field of view of a camera used in a scanner for scanning images onto printed circuit board substrates, the method comprising:
(a) providing a pattern of holes;
(b) imaging the pattern with the camera; and
(c) determining correction factors for locations in the camera field of view
Optionally, the pattern comprises a two dimensional pattern. Optionally, calibrating includes adjusting the spatial orientation of the imager with respect to the scanner. Optionally, calibrating includes compensating for differences in magnification at various parts of the field of view of the imager. Optionally, calibrating includes compensating for distortion in the field of view of the imager.
There is further provided, in accordance with an exemplary embodiment of the invention, a method of correcting alignment between a scanner portion of a direct writing scanner and an imager thereof, the method comprising:
(a) providing a transformation between a scanner coordinate system and an imager coordinate system;
(b) providing an object whose location is measurable in both the scanner coordinate system and in the imager coordinate system;
(c) measuring the location of the object in the scanner coordinate system;
(d) measuring the location of the object in the imager coordinate system; and
(e) correcting the transformation based on the measured locations in the two coordinate systems.
Optionally, correcting comprises:
transforming the measured location in a first one of the coordinate systems to the other coordinate system;
determining a difference between the location of the object as measured in the other coordinate system and the location of the object measured in the first coordinate system and transformed into the other coordinate system; and
correcting the transformation responsive to said difference.
Optionally, the object is a circularly symmetrical object.
Exemplary embodiments of the invention is described in the following sections with reference to the drawings. The figures are generally not to scale and the same or similar reference numbers are used for the same or related features on different drawings.